In a large bowl, whisk together the mashed banana, peanut butter, and eggs until smooth. Whisk in the vanilla and maple syrup.

Sprinkle the baking soda, cinnamon, protein powder, flaxseed, and chia seeds over the top. Stir to combine.

Fold in the oats, walnuts, chocolate chips, and cranberries. The batter will look very liquidy.

Place the bowl in the refrigerator to chill and set for at least 4 hours, or for the thickest cookies, cover with plastic and refrigerate overnight.

When ready to bake, place a rack in the center of your oven and preheat the oven to 375°F. Line a baking sheet with parchment paper or a silicone baking mat. With a large cookie scoop or spoon, portion the batter by 1/4 cupfuls onto the prepared cookie sheet. If needed, shape them lightly with your fingers so that they are round and very slightly flat on top.

Bake for 9 to 12 minutes, until the cookies feel nearly set on the top and edges and a toothpick inserted into the center comes out clean (they will look underbaked but will set up more on the baking sheet). Let cool on the pan for 15 minutes, then transfer to a wire rack to finish cooling completely.